Plaster gives interior walls and ceilings a hard, smooth finish. Whether you apply a thin veneer coat over blue board or a thicker base coat on masonry, the quantity depends on the area, the coat thickness and the product. This calculator gives the weight of plaster, the number of bags and the cost.
The formula
Plaster (kg) = net area (m²) × thickness (mm) × consumption (kg per m² per mm) × (1 + waste)
Most gypsum plasters use about 0.8 to 1.0 kg of dry powder per m² for each millimeter of thickness. The calculator converts square feet and inches for you.
Example
A room with 400 sq ft of walls and ceiling and 40 sq ft of doors and windows has 360 sq ft to cover. A 1/8 in veneer coat at 0.9 kg per m² per mm, with 10% waste, needs about 232 lb of plaster: 5 bags of 50 lb. Each bag covers about 78 sq ft at that thickness. At $25 a bag, the material costs $125.
Typical thicknesses
| System | Thickness |
|---|---|
| Veneer plaster over blue board, one coat | 1/16 to 3/32 in |
| Veneer plaster, two coats | about 1/8 in |
| Base-coat plaster on masonry or lath | 3/8 to 5/8 in |
| Skim coat over existing plaster | 1/16 in or less |
Applying plaster
- Prepare the surface: clean it, remove loose material and apply a bonding agent on smooth or porous surfaces.
- Mix only what you can use within the working time on the bag, usually 45 to 90 minutes.
- Apply with a steel trowel, keep a wet edge and work from top to bottom.
- Trowel again as the plaster starts to set for a hard, smooth finish.
- Let it dry fully before painting, and use a primer suited to new plaster.
Plaster or drywall?
Drywall with taped joints is faster and cheaper for most new walls. Plaster is harder, more resistant to dents, better at sound control and the right choice for repairing older plaster walls.
Limits
Real consumption depends on how flat the surface is: uneven walls can take much more plaster in the low spots. Check the coverage on the product bag and adjust the consumption if needed.